Efficacy and safety of Ginkgo biloba extract as an adjuvant in the treatment of Chinese patients with sudden hearing loss: a meta-analysis

Abstract Context Ginkgo biloba Linn (Ginkgoaceae) [leaves extract (GBE)] is authorized for the treatment of sudden hearing loss (SHL); however, its clinical feasibility in SHL has not been thoroughly investigated. Objective To evaluate the efficacy and safety of adjuvant GBE in the treatment of SHL. Materials and methods We used PubMed, EMBASE, Web of Science, Cochrane Library, China National Knowledge Infrastructure, Wanfang, Chinese Scientific Journal Database, China Biomedical Database for literature research, starting from inception to 30 June 2022. The key terms: Ginkgo biloba extract, Sudden Sensorineural Deafness. This meta-analysis contained randomized controlled trials that compared the safety and efficacy of the combination of GBE and general treatments (GT) with GT alone for SHL. The extracted data were analyzed using Revman5.4 software with risk ratio (RR), 95% confidence intervals (CI) and mean difference (MD). Results Our meta-analysis included 27 articles with a total of 2623 patients. The results revealed that the effects of GBE adjuvant therapy was superior than GT (total effective rate: RR = 1.22, 95% CI: 1.18–1.26, p < 0.00001), the pure tone hearing threshold (MD = 12.29, 95% CI: 11.74–12.85, p < 0.00001) and hemorheology indexes (whole blood high shear viscosity: MD = 1.46, 95% CI: 0.47–2.44, p = 0.004) after treatment were significantly improved compared to non-treatment, while there was no significant difference as for hematocrit (red blood cells) (MD = 4.15, 95% CI: −7.15–15.45, p = 0.47). Conclusion The efficacy of GBE + GT for the treatment of SHL may be more promising than GT alone.


Introduction
Sudden hearing loss (Byl 1984;O'Malley and Harnes 2008;Wen et al. 2020;Wang and Ma 2022), known as sudden sensorineural hearing loss, is a common emergency in otolaryngology. Its clinical symptoms include unilateral hearing loss, accompanied by tinnitus, dizziness, nausea and others. Although the etiology and pathogenesis of SHL are still not clear until now, some researchers (Yu and Yang 2015;Beckers et al. 2021;Ricciardiello et al. 2021;Si, Liu, et al. 2022) attribute it to viral infection, circulatory system dysfunction, immune dysfunction, etc. There is still no standard treatment strategy; treatment for sudden deafness is basically comprehensive, and the application of drugs in nutritive nerve and circulatory improvements is common (Li et al. 2016;Chandrasekhar et al. 2019).
Ginkgo biloba Linn (Ginkgoaceae) leaves extract (GBE) is an active ingredient extracted from the dried leaves of Ginkgo biloba (Yang et al. 2016;Barth et al. 2021), with the effects of promoting blood circulation and removing blood stasis, activating the collaterals to relieve pain, warming the lungs and relieving asthma, removing turbidity and reducing lipid. It is widely used for the collateral obstruction, chest paralysis and heartache, stroke hemiplegia (Zhang et al. 2021). GBE contains Ginkgo flavonoids, quercetin, ginkgolides, organic acids, and other components , which exert a variety of pharmacological effects, such as dilating blood vessels, regulating blood lipids, antagonizing platelet activating factor, protecting ischemic injury, anti-inflammatory, and antitumor (Liu et al. 2014). It also has definite curative effects for the treatment of coronary heart disease, cerebral thrombosis, cerebral ischemia, cerebral dysfunction, sequelae of brain trauma, nervous system diseases and scavenging oxygen free radicals (Gai et al. 2017;Liu et al. 2021;Xiao et al. 2022).
GBE has the effect of improving inner ear circulation (Kandiah et al. 2021), which is suitable for the diagnosis and treatment of tinnitus, vertigo, hearing loss and neurological disorders. Some studies (Gao et al. 2015;Zeng and Liu 2020;Qu and Gao 2021) have shown that it also has a specific therapeutic effect on SHL, but the sample size included in each study is small, and such experimental results are not objective and comprehensive, so it impacts on the reliability of the combination effect and the scope of the clinical promotion and application is not ideal. We performed this meta-analysis to evaluate the efficacy, safety of GBE, and provided scientific evidence to the design and implementation of SHL and scientific basis for its clinical practice.

Outcome definitions
The main outcomes were the total effective rate and cure rate, and the secondary outcomes were pure tone hearing threshold, hemorheology and adverse drug reactions (ADR). The cure standard was that the patients with SHL basically to the original level. The ineffectiveness means that the patients with SHL had no obvious improvement or further deterioration. Total effective rate ¼ (number of all cases-number of ineffective cases)/the total number of patients Â 100%. The cure rate ¼ the number of cured cases/the total number of patients Â 100%.

Data extraction and quality assessment
The following data were extracted from eligible literature: the first author; year of publication; number of cases; age of patient; intervention; GBE dosage; duration of treatment and ADR.
The final articles included in our meta-analysis were independently screened by two reviewers. The titles and abstracts of the remaining researches were reviewed after excluding duplicate studies. The full text of the remaining studies was independently reviewed by two reviewers. If two reviewers disagreed on the article that is eventually included, a third reviewer will resolve the dispute.
According to the bias risk assessment recommended by Revman5.4, the evaluation criteria included seven domains of evaluation: (a) random sequence generation (selection bias); (b) allocation concealment (selection bias); (c) blinding of participants and personnel (performance bias); (d) blinding of outcome assessment (detection bias); (e) incomplete outcome data (attrition bias); (f) selective reporting (reporting bias); (g) other bias.
The Cochrane Correspondence Network RCT was used to assess each project in terms of low risk (þ), unknown risk (?) and high risk (À). The quality evaluation of retrieved studies was conducted by group discussion.

Statistical methods
Revman5.4 software was used for this meta-analysis. The relative risk (RR) and its 95% confidence interval (CI) of dichotomous data were used as the effect analysis statistics, and the variations in pure tone hearing threshold and hemorheology were expressed as mean difference (MD) with 95% CI of continuous data. I 2 statistics and chi-square test were used to assess the statistical heterogeneity. Values of p > 0.1 or I 2 < 50% denoted the existence of low heterogeneity, the fixed-effect model was chosen; otherwise, the random-effects model was adopted. The p-value less than 0.05 was considered statistically significant. A funnel plot was used to test for publication bias.

Search results
According to the search strategy, a total of 346 relevant studies were included in this analysis. Among them, 5 articles were included in PubMed, 2 articles in EMBASE, 12 articles in Web of Science, 3 articles in Cochrane Library, 85 articles in CBM, 65 articles in CNKI, 98 articles in WanFang, and 76 articles in VIP. After removing duplicate articles and research, 141 articles were retained. Then, 87 articles were excluded by reviewing the titles and abstracts. Subsequently, 27 articles were excluded after assessment of the full text, on account of the following: incomplete data for experimental group or control group (n ¼ 5), no statical data (n ¼ 8), no complete data sets (n ¼ 10), inconformity to the inclusion criteria (n ¼ 4), finally 27 eligible articles (Wang and Li 2008;Su 2013;Han et al. 2015;Liang et al. 2017;Shi 2017;Wang 2017;Abu et al. 2018;Fu 2018;Meng et al. 2018;Xie 2018;Ye et al. 2018;Yu and Xu 2018;Zhao et al. 2018;Zhang GJ et al. 2019;Zhang HJ et al. 2019;Zhang JY et al. 2019;Dong 2020;Liang 2020;Lu et al. 2020;Xin et al. 2020;Huang and Luo 2021;Jia et al. 2021;Liu 2021;Tang 2021;Wu and Run 2021;Sun 2022) were included in our metaanalysis ( Figure 1).

Patient characteristics
All 27 studies with a total of 2623 patients of SHL were RCTs, including 1312 patients in the experimental group and 1311 patients in the control group. The experimental group was treated with Ginkgo biloba extract combined with other methods, and the control group was treated with other basic treatments. Randomization was mentioned in all 27 studies, and the sample size of a single RCT was 100 at most and 15 at least. Ginkgo biloba tincture (Beijing China Resources High-tech Natural Medicine Co., Ltd.) was mentioned in 2 studies (Fu 2018;Yu and Xu 2018), Ginkgo biloba extract injection (Taiwan Jisheng Chemical Pharmaceutical Co., Ltd.) in 10 studies (Han et al. 2015;Abu et al. 2018;Meng et al. 2018;Ye et al. 2018;Dong 2020;Lu et al. 2020;Xin et al. 2020;Huang and Luo 2021), Ginkgo biloba extract injection (YOUCARE Pharmaceutical Group Co., Ltd.) in 7 studies (Liang et al. 2017;Wang 2017;Zhao et al. 2018;Jia et al. 2021;Liu 2021;Tang 2021;Wu and Run 2021), while no specific information of GBE was described in 7 studies (Wang and Li 2008;Su 2013;Shi 2017;Xie 2018;Liang 2020;Sun 2022). The characteristics of the studies that are included in this meta-analysis are summarized in Table 1.

Outcome measures
Total effective rate Twenty-seven studies were included in this section, with 1312 patients in the experimental group and 1311 patients in the control group. No statistical heterogeneity was shown (p ¼ 0.99, I 2 ¼ 0%), and a fixed-effects model was used for meta-analysis. The results showed that there were significant differences between the experimental group and the control group. The patients in the experimental group showed a higher total effective rate than those in the control group (RR ¼ 1.21, 95% CI: 1.17-1.26, p < 0.00001) (Figure 4).

Cure rate
Twenty studies (Wang and Li 2008;Su 2013;Liang et al. 2017;Shi 2017;Wang 2017;Abu et al. 2018;Meng et al. 2018;Ye et al. 2018;Yu and Xu 2018;Zhao et al. 2018;Lu et al. 2020;Xin et al. 2020;Huang and Luo 2021;Jia et al. 2021;Tang 2021;Wu and Run 2021;Sun 2022) were included, with 994 patients in the experimental group and 994 patients in the control group, while the remaining 7 studies were no cured data. A fixed-effect model was applied for meta-analysis as there was no statistical heterogeneity (p ¼ 0.95, I 2 ¼ 0%). The results showed that there was a significant difference between the experimental group and the control group. The patients in the experimental group showed a better cure rate compared with the control group (RR ¼ 1.60, 95% CI: 1.40-1.84, p < 0.00001) ( Figure 5).  Jia et al. 2021;Sun 2022) were included, with 720 patients in the experimental group and 719 patients in the control group, while others were no pure tone hearing threshold data. A random-effects model was used to describe this indicator due to the high statistical heterogeneity between the two groups (p < 0.00001, I 2 ¼ 94%), according to the original data, pure tone hearing threshold improvement was calculated with standard deviation (SD). The experimental group could significantly improve the hearing results (MD ¼ 11.12, 95% CI: 8.41-13.84, p < 0.00001) ( Figure 6).

Hemorheology
Thirteen studies (Su 2013;Shi 2017;Abu et al. 2018;Meng et al. 2018;Ye et al. 2018;Zhao et al. 2018;Dong 2020;Lu et al. 2020;Jia et al. 2021;Liu 2021;Tang 2021;Wu and Run 2021) were included, the remaining 14 articles were no information on hemorheology. Hemorheology assessments were conducted such as whole blood high shear viscosity, whole blood  2021) reported ADR during the therapy, mainly manifested as nausea and vomiting, fever, digestive disorders, and sleep problems, but no serious adverse events were reported. Since the specific adverse reactions observed in each study were different and the number of the same adverse reactions was small, the assessments were not carried out in this analysis, however there was significant difference between two groups based on the number of adverse reactions (RR ¼ 0.68, 95% CI: 0.47-0.97, p ¼ 0.04) (Figure 7).

Publication bias
In order to evaluate the publication bias that might be produced in this meta-analysis, funnel plots and Egger's test were examined. The results showed that the funnel plots of the total effective rate, cure rate and adverse reactions were asymmetrically distributed (Figures 8-10), suggesting that the publication bias may exist, and Egger's test (p < 0.0001) also indicated the possible existence of publication bias.

Discussion
SHL is sensorineural hearing loss with the characteristics of sudden loss or even disappearance. But the pathogenesis of SHL has   not been clear until now. It may cause permanent deafness without timely treatment, which leads to great distress or inconvenience to patients. It is reported that inner ear microcirculation disturbance, insufficient blood supply, viral infection, immune imbalance, and rupture of the membrane labyrinth may be correlated with the pathology of SHL (He 2018; Liu and Zhang   2018; Compagnone et al. 2022;Khasanov et al. 2022). Excessive social pressure and negative life events are important factors inducing sudden deafness, so psychological factors are also one of the potential factors of sudden deafness. In addition, ischemia, hypoxia and microcirculatory disorders in inner ear can also lead to vasospasm, thrombosis, increased blood viscosity, slow hemodynamic changes, increased oxygen free radicals or decreased free radical scavenging enzyme activity, leading to cochlear receptor ischemia, spiral nerve degeneration, and ultimately hearing impairment. Many viruses, such as measles virus, herpes simplex virus and cytomegalovirus, can incubate in the nervous system. The herpes simplex virus can infect the auditory pathway and nerve, especially through blood circulation into the inner ear, inducing cochlear microcirculation disorders and sudden deafness (Kuhn et al. 2011;Chen et al. 2019). GBE is a traditional Chinese medicine preparation extracted from Ginkgo biloba leaves. The main active ingredients contain ginkgolides and flavonoid glycosides, which can inhibit the formation of ear thrombus, scavenge oxygen free radicals, improve vascular microcirculation, and reduce blood viscosity (Wang and Yang 2001;Wang and Li 2009;Zhao 2010;Barth et al. 2021). It can effectively promote inner ear microcirculation, help patients recover from hearing dysfunction, accelerate the relief of tinnitus and vertigo, which exerts significant pharmacological activity on SHL. Recent studies have shown that ginkgolides contained in ginkgo leaf preparations are antagonists of platelet activating factor (PAF) (Smith et al. 1996), which can prevent platelet aggregation and thrombosis induced by PFA, reduce blood viscosity and improve blood rheology. GBE exerts significant antioxidant activity (Singh et al. 2019;Bohlken et al. 2022), which can improve the activity of superoxide dismutase (Barth et al. 2021), accelerate the scavenging of oxygen free radicals caused by ischemia, and protect cell tissues. GBE also has vasodilator effect, it can stimulate the production of endothelium-derived relaxing factor and prostacyclin, promote the relaxation of vascular smooth muscle, which could maintain good arteriovenous tension, and increase the blood flow in and around the injury spot . GBE dilates the auricular arterioles, increases the blood flow of the inner ear, enhances the compensatory function of the inner ear, improves tissue metabolism, alleviates labyrinthine artery edema, and accelerates the disappearance of clinical symptoms (Spiegel et al. 2018).
Our analysis showed that GBE can improve the total effective rate and cure rate, it was also reported that GBE had been applied to SHL and exerted a strong effect (Burschka et al. 2001;Si, Yu, et al. 2022), with pure tone hearing threshold improved significantly, it was consistent with our results. In the early studies (Spiegel et al. 2018;Radunz et al. 2020;Barth et al. 2021), GBE had an obvious effect in relieving tinnitus and improving cochlear blood flow, while our meta-analysis showed that GBE can improve pure tone hearing threshold and hemorheology, our results are in line with the former studies. Therefore, treatment of SHL with GBE adjuvant can be practicable because of its efficacy and safety. However, this study has some limitations. First, some literature does not report specific randomized control trials, which may cause random sequence generation bias, the details were insufficient, such as randomization methods, allocation concealment, performance bias, attrition bias, reporting bias, some literature had high risk factors in quality evaluation, so it has a certain impact on the strength of the evidence. Second, the literature included in this study is restricted to the region of China, which may cause ethnic and regional bias. Finally, no long-term prognosis (such as overall survival, progression-free survival and recurrence rate) was reported in the literature, making it difficult to analyze the overall safety and efficacy. Therefore, large-scale, multi-center, randomized, double-blind and other high-quality clinical randomized trials are in demand in the future (Moher et al. 2009), and combining the characteristics of GBE in terms of dosage, duration of treatment, and incidence rate of adverse reactions, and comprehensively consider long-term treatment effects and drug safety and effectiveness, so as to provide strong evidence for further clinical practice.

Conclusion
The results of our meta-analysis showed that adjuvant therapy with GBE may be better than no GBE, the total effective rate and cure rate are significantly improved, the pure tone hearing threshold and hemorheology indexes are significantly improved with treatment, and the rate of adverse reactions is reduced. Based on the results of our analysis and the theoretical basis of SHL, GBE may be a perfect complementary and alternative therapy strategy. However, the low quality of some articles resulted in the potential risk of bias, which affected the reliability of this study to some extent. Therefore, the long-term efficacy and safety of GBE on SHL still need to be verified by large multicenter and carefully designed rigorous RCTS to provide reliable evidence for the efficacy of GBE as an adjunct on SHL.

Author contributions
Zhang K and Zhang H, drafted and reviewed the concept, Yuan C and Zhang K independently performed searches, and Zhang H resolved any dispute, if necessary, Zhang K and Zhang H carried out data extraction and quality assessment, Yuan C performed this analysis, Sun CC and Yuan C polished and revised the paper. All authors approved the final version of the manuscript and approved the submitted version.

Disclosure statement
No potential conflict of interest was reported by the author(s).

Funding
The author(s) reported there is no funding associated with the work featured in this article.